I saw in a few places that when they write Malachi, in parentheses they write Ezra. Does that mean that some people agree that they are one person?
Yes, there is such an opinion in the Talmud (Megillah 15a):
"It is taught in a baraita: Rabbi Yehoshua ben Korḥa said: Malachi is in fact Ezra."
This view has been accepted by many, although there are those that disagree, including right there in the Talmud.